This invention relates to an electromagnetic clutch, particularly an electromagnetic clutch for selectively transmitting rotation of an automobile engine to a compressor used for automobile cooling apparatus.
This kind of electromagnetic clutch usually comprises a clutch disc connected to a rotary shaft; a rotor or pulley means including a belt receiving portion, an annular portion facing the clutch disc with a gap and a cylindrical bearing receiving portion; and a stator which is secured to the compressor and includes an electromagnet and a cylindrical portion rotatably supporting the rotor through a bearing. The stator of this type is shown in U.S. Pat. No. 3,703,227, wherein the stator except windings, that is, a stator frame has a flange (71) and ring (75) as a U-shaped core for containing a winding therein; a flat portion 74; and a small ring (76). The small ring (76) supports the bearing receiving portion of the rotor through the bearing, and the outer face of the bearing receiving portion faces the inner face of the ring (75) with a small air gap to establish a magnetic flux passage, so that the inner face of the ring (75) and the outer face of the small ring (76) must be precisely finished. Further the flange ( 71) face also faces the stator with a small gap to establish a magnetic flux passage, so that a precise relation between the flange (71), the ring (75) and the small ring (76) must be made.
The stator flame comprises three parts and need two junctures, so that assemblying of the stator flame is laborious.
As stated above, the stator flame has a plurality of faces which each belong to different parts and need accurated concentricity to each other. Therefore, on bases of one of the faces the other faces need be machined precisely, so that the machining is laborious.
Further, the stator flame is made such that a part of the stator flame bridging from the flange (71) to the small ring (75) is made of one piece of low carbon steel, and the small ring (76) also is made low carbon steel since the piece is junctioned by friction welding and the juncture must be strong. Therefore, since the magnetic circuit results in magnetic flux passing through the small ring, a resultant loss of magnetic flux amounting to about 17-18% occurs whereby the electromagnetic clutch effects decreased performance.